Using neuroimaging techniques to find biomarkers of autism spectrum disorder (ASD) and related social difficulties will allow for earlier detection of risk: a critical component of identifying which infants need preventive treatment. Neuroimaging may also offer a more sensitive method of predicting and assessing treatment response than focusing only on observable behavior. However, we first need to improve our understanding of typical brain development to identify neural markers that predict individual differences in social behaviors. These neural markers can then become targets for the study of biomarkers of ASD. Better understanding the neural differences associated with ASD and related social difficulties will help to guide the development of treatments that are closely matched to biological areas of deficit and provide promising regions of interest for studies utilizing neuroimaging to predict and assess treatment response. The current proposal is a multi-level (brain function and behavior), longitudinal neuroimaging study of 60 typically developing infants during a critical period in social development. The study will utilize functional near infrared spectroscopy (fNIRS) to measure brain functioning in response to both novel (live social interaction) and well-validated (biological motion) social stimuli at 6 months of age. Identified neural correlates of social stimui will then be applied to predict individual differences in key areas of social functioning in these same infants at 12 months. The applicant's overarching career goal is to conduct research that helps to prevent deficits in social- emotional functioning before they reach clinically impairing levels. The proposed fellowship training is an integral step in this career path. The applicant wil receive intensive training in developmental neuroimaging techniques under the mentorship of a leading researcher in the neurobiology of social cognition and ASD. This project, which combines clinical and developmental research using behavioral and neuroimaging techniques, will provide an ideal vehicle for the trainee to develop as an independent researcher in the field of translational developmental neuroscience, so that her research program can help bridge the gaps between social development, neural systems, and clinical research.